Date of Graduation

12-2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Physics (PhD)

Degree Level

Graduate

Department

Physics

Advisor/Mentor

Churchill, Hugh O.H.

Committee Member

Hu, Jin

Second Committee Member

Barraza-Lopez, Salvador

Keywords

Hermatic cell; inert environment; van der Walls; Optical analysis; device fabrication

Abstract

This thesis describes measurements on hybrid material systems involving two dimensional (2D) materials and phenomena along with the development of a small, hermetically sealed cell. The hermetic cell is designed to assist with analyzing sensitive 2D materials outside of an inert environment. When working with van der Waals materials that are especially sensitive to oxygen or water, it can be difficult to identify usable thin flakes without exposing them to air. To help preserve materials for analysis in air, a capsule was designed that isolates the material in an inert environment. Although the capsule is hermetically sealed, the encapsulated material remains accessible to optical analysis; analysis that is crucial to device fabrication. The first system is a Josephson junction field effect transistor (JJ-FET) fabricated in epitaxial Al-InAs. The supercurrent through the junction in this system can be tuned by applying an external electric field with a gate. Typically, the gate dielectric is a thick oxide layer (50 nm) but the devices described here are able to achieve full supercurrent tunability, and comparable quality, with only a 5 nm thick layer of mechanically exfoliated 2D hexagonal boron nitride. The second set of measurements are on a superconductor/semiconductor devices based on germanium quantum wells with epitaxial Al contacts. These serve as the first steps toward realizing a many-qubit system that can leverage the high mobility, spin properties, and fabrication advantages of germanium. These measurements are of the magnetotransport characteristics of MBE grown, strained germanium quantum wells embeded in a SiGe heterostructure. The devices discussed here demonstrate suitable electrical properties for Josephson junction development towards the goal of a gatemon qubit.

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